Distribution of many liquid products, in particular petroleum products such as gasoline and fuel oil, from a bulk storage plant to retail operations for consumers is accomplished by means of tank trucks or transport trailers. These vehicles are filled with a liquid by various methods, one of which is called top loading.
In top loading the vehicle is positioned next to a loading rack which is equipped with a system for transferring the liquid products from the storage tank to the tank truck or transport trailer. These systems generally comprise what is known as a loading arm which consists of a boom that is pivotally connected to the storage tank and can be moved about the pivot to attach the flange at the end thereof to the mating flange on the truck or transport trailer.
In this operation the operator of the vehicle climbs on top of the vehicle, opens the manhole, and swings the loading arm into position over the flange on the manhole. Under the old method of top loading, the diameter of the nozzle attached to the line on the loading arm that extended into the manhole was considerably smaller than the diameter of the manhole so that the operator could observe the level of the liquid rising within the vessel as he loaded and could control his inputs so as to obtain a maximum capacity of the vessel without overfilling.
In recent years there has been a considerable change in this method due to the regulations of the Environmental Protection Agency regarding air pollution. At present, the boom and flange system includes a vapor recovery system that insures that no vapor from the gasoline or other volatile liquid supplied to the tank truck or transport trailer is released into the atmosphere.
These devices differ in design. One of the most common is a structure in which the vapor return head is mounted on the end of the loading arm as part of a plate which seals off the flange in the manhole in the tank to be filled. The sealing of the manhole prevents the operator from observing the liquid level in the vessel as he is loading. A preset meter system has been used in an attempt to solve this problem. In addition, various complex electronic and pneumatic systems have been devised to prevent the tank truck or transport trailer from being overfilled and still permit the vehicle to be loaded to full capacity.
These systems require complex electrical or pneumatic installations at the loading rack and also require explosion-proof equipment. Automatic control valves or preset meters may also be installed to operate in conjunction with the overfill prevention equipment.
The preset meter system is unsatisfactory in that, if the operator underestimates the volume of liquid contained in the vessel before loading operation begins, he runs the risk of overfilling his tank. If he overestimates the liquid present in the vessel, he will underfill the tank and proceed on his delivery route with less than a full tank of liquid.
A control device such as the electronic liquid lever senser that will automatically shut off the valve and not permit any more liquid to fill the tank also has certain inherent disadvantages. If the device malfunctions, the operator would have no way of knowing that the tank is full and would still run the risk of overfilling. If, on the otherhand, the control device malfunctions in the closed position, it will shut down his operation until the control device can be bypassed.
The present invention satisfactory overcomes this problem by permitting the operator to observe the liquid level in the tank so that overfilling can be prevented, and yet the tank can be loaded to full capacity.
An object of the invention is to provide a visual level indicator system that is a simple mechanical device which does not require extensive electrification, pneumatic operation, or complex explosion-proof integrity at the loading rack.
It is another object of the invention to provide a mechanical system that is much less complex than the electronic systems and one that is less subject to malfunction.
It is another object of the invention to provide a system that will permit the operator to load his vessel even in the event of a malfunction.